Method and apparatus for reproducing television pictures



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Dec. 25, 1945. F. E. FISCHER 7 ,4

METHOD AND APPARATUS FOR REPRODUCING TELEVISION PICTURES SUB T TE Q M XR Filed May 11, 1940 s Sheets-Sheet 1 I 18 I 23 l l l I I J I l I l r; w I (19m I l I I I I i I l I 1 I 1 l I I I l n Mum... hm

INVENTOR 1 fi'EF/SCHER BY ATTORNEYS 25; 1945. F, E, FISCHER 2,391,450

METHOD AND APPARATUS FOR REPRODUCING TELEVISION PICTURES Filed May 11, 1940 6 Sheets-Sheet 2 18 I l 23 l I l I II I 1 I I l l l I I I l l I l I I 1 I 1 I Z :ll I II I l I I 0 4 t I 5 D I INVENTOR I EF/SCfiE ATTORNEYS Dec. 25, 1945.

F. E. FISCHER Filed May 11, 1940 METHOD AND APPARATUS FOR REPRODUCING TELEVISION PICTURES 6 Sheets-Sheet 5 r r 7 INVENTOR 5 FE F/SCHER i BYWM ATTORNEYS 25, 1945. FlsCHER 2,391,450

METHOD AND APPARATUS FOR'REPRODUCING TELEVISION PICTURES Filed May 11, 1940 6 Sheets-Sheet 4 INVENTOR FE/ /SC/ /ER 2 G9 7 ATTORNEYS Dec. 25, 1945. F. E. FISCHER 2,391,450

METHOD AND APPARATUS FOR REPRODUCING TELEVISION PICTURES Filed May 11, 1940 6 Sh eets-Sheet 5 INVENTOR FfF/SCfi/SQ BY :lmmmlm *hhl llhl l ATTORNEKS Dec. 25,

1945- F. E. FISCHER 2,391,450

METHOD AND APPARATUS FOR 'REPRODUCING TELEVISION PICTURES Filed May 11, 1940 6 Sheets-Sheet 6 INVEN'ITIJR 1 FE HSCHER ATTORNEYS Patented Dec. 25, 1945 OFFICE METHOD AND APPARATUS FGR REPRO DUCING TELEVISION PICTURES Friedrich Ernst Fischer, Zurich-Erlenbach, Switzerland Application May 11, 1940, Serial No. 334,520 In Switzerland November 8, 1939 9 Claims.

At the present time, the reproduction of television pictures is effected almost exclusively by cathode y tubes in combination with luminescent or thermal screens. Whereas all the other ponentsv of a television installation are readily capable of being employed also for th p du ti n f la e pictures, such as pictures having dimensions comparable with those of present-day cinematograph projection, known screens are not able to provide larger pictures with suflicient brightness. This is to be attributed to the fact that the brightness values essential for a large projection cannot be reached or can only be imperfectly attained with the known fluorescent materials. Moreover, the thermal screens did not bring any substantial technical advance in this direction. It has also already been proposed to build up the screen it self from innumerable small light sources and then to control the latter, but no practical results were produced by this means. It is thus apparent that, according to the present day state of the art, satisfactory large area television pictures cannot be reproduced,

The object of the present invention, therefore, is to provide a method and a means whereby larger television pictures are capable of being reproduced with suflicient light intensity.

The method according to the present invention is carried out with a cathode ray tube and separate light source and is characterised by the feature that in the optical path of the rays between the separate light source and the projection screen, there is arranged a medium which is extended to form a fiat surface and which is portrayed on the projection screen by an objective and. due to electrostatic or inverse piezoelectric forces which are produced by electrical charges with the aid of the cathode ray tube, is deformed uniformly with the picture brightness, whereby a point-by-point control of the light emanating from the separate light source takes lace. p Due to the electrostatic or piezo-electric forces, the result is attained that the medium is deformed to form numerous small lenses or small curved mirrors. Conveniently, the deformation is so selected that a lens raster or mirror raster is formed.

The lenses or curved mirrors formed by the deformation can be of any-type, i. e., cylindrical lenses, concave or convex mirrors, concave cylindrical or convex cylindrical mirrors can be produced, which then again form a raster over the whole area of the medium. The formation of lenses or mirrors is naturally dependent upon the nature of the medium employed. If lenses are to be formed, the medium must be transparent, whereas for the formation of mirrors, a surface reflection of the medium is essential. The deformation of the medium is now caused by opposite charges on both sides thereof. The charges are applied on one side by the electron beam so that the place on the medium which is being swept over by said beam forms a small lens or a small mirror. A light beam emanating from a separate light source is now thrown simultaneously or at another point of time on to the same place and is projected, suitably deflected, on to the projection screen.

It will now be apparent that for producing the television picture, a charge distribution corresponding to the brightness values thereof must take place on the medium in order to obtain the corresponding deformation. In order that the forces necessary for the deformation shall be reached in each case, the medium can be subjected to the action of an external field.

If the charging by the cathode ray and the illumination of one and the same place On the medium take place simultaneously, then no further devices are necessary; the light beam is thrown on to the projection screen. However, if the charging and illumination do not take place simultaneously, then mechanical diaphragms or mirrors moved in synchronism with the periodic movement of the cathode ray are to be provided for covering the elements of the medium which are not being illuminated or charged at that time, i. e., interrupt the path of the rays from these elements to the projection screen. In this case, the individual pictures are conveniently stored one after the other on different plates of the medium and projected.

The result f the continuous changing of the television picture is that one and the same raster element always receives other charge values. The charge once applied must, therefore, either be removed or brought to a new value. The cancellation of the charge which has been applied can be effected periodically by a separate cathode ray or even photo-electrically.

In addition, the charges which have been applied can, after projection of the picture has taken place, also be removed in a simple manner by the medium-itself having a suitable conductivity, whereby the charges are discharged.

A further possible way of varying the charges on the medium is by arranging that the side of the medium which is swept by the cathode ray emits secondary electrons, this being attained by suitable treatment of the surface. This secondary emission causes the elements which are individually bombarded by the electron ray to receive, each according to its control, another charge, since when the velocity of the electron beam is high, fewer electrons escam by secondary emission than are applied by the electron beam and thus the element becomes negative, whereas when the velocity of the electron beams is low, more electrons escape by secondary emission than are applied by the electron beam, and thus the element becomes positive.

In many cases, e. g., when the charges are discharged by electrical conduction of the medium and the electron beam always takes up a new charge, it is, however, advantageous if no secondary emission takes place. Theoretically, this can be attained by suitable selection of the final velocity of the cathode ray or of the medium. In practice, however, it is scarcely possible to obtain complete elimination of the secondary emission. It is therefore convenient to eliminate the secondary electrons which still occur despite the precautions already mentioned and which, as so called "stray electrons, can cause an undesired locally different charging of the medium, by the application of a suitably directed external field to the surface of the medium.

Generally speaking, it is usual in the television art to split up the picture into a line raster and to produce this raster by rapid horizontal and slow vertical periodic deflection of the electron beam. In this case, the brightness values of the individual picture points or raster elements are produced by control of the electron beam.

This control of the electron beam can take place in different ways and is, in the case of the present invention. dependent upon the method selected for the change of potential of the separate raster elements. Thus, for example, with cancellation at a given time of the charge values existing on the medium and application of new values, a si... ple intensity control of the cathode ray is suitable, since thereby each raster element receives a charge corresponding to the intensity of the oath- Ode ray. On the other hand, when the potential of the raster elements is changed with the aid of the secondary emission, the electron beam must be controlled as regards velocity. Finally, it is also possible by suitabl variation of the size of the cathode spot on the medium or of the intensity distribution of the cathode ray on the medium, to apply to the medium a charge distribution which corresponds to the different brightness values of the picture.

As already mentioned, a raster consisting of lenses or mirrors is formed on the medium. This raster-like deformation of the medium is most easily attained by a corresponding raster-like distribution of the charges on the medium. It is here to be mentioned that this raster produced by deformation is preferably not identical with the line raster traversed by the electron beam, but is finer, because in this Way a better picture reproduction is possible.

Now, since the deformation raster is finer than the line raster described by the electron beam, the latter must be separated into a plurality of beams operating closely adjacent one another if the deformation raster is located in the line direction, or else the deformation raster must lie in a direction other than the line direction, preferably perpendicularly thereto. Such a fine deformation o charging raster disposed perpendicularly of the line direction can, for example, take place by controlling the electron beam with a high frequency carrier wave, whereby a whole number of carrier wave lengths fall on one line length. There are formed in this way, along each line, periodic charge accumulations which are located closely alongside one another and which, seen from line to line, ie perpendicularly together and thus form a fine perpendicularly disposed deformation raster. If, on the contrary, no whole number of carrier wave lengths fall on one line length, the deformation raster is at an inclination.

If, in addition, the carrier wave is now modulated with the television signal, a charge distribution or deformation which is finely rastered cor responding to the brightness values of the television picture appears on the medium.

The means for carrying into effect the method which has been outlined above consists essentially of a cathode ray tube with at least two beamdefiecting systems and at least one control device for the intensity, intensity distribution or velocity of the cathode ray, in which tube is arranged, as a screen, a medium having at least one electrically conducting electrode, said medium being extended to form a flat surface and being deformable by electrostatic or plezo-electrlc forces, and a separate light source, from which the light is projected, by lens and mirror systems, on to or at least once. through the medium of he cathode ray tube and thence, by way of at least one objective, on to the projection screen, the arrangement being so contrived that no light from the separate light source reaches the projection screen from raster elements, the deformation of which corresponds to the brightness 0.

An exhaustive description of the method and of the apparatus will now be given with reference to the accompanying drawings.

Figs. 1 to 8 show varlous constructional examples of the arrangement according to the invcr ion; while Fig. 9 shows the relationship of the secondary emission factor to the electron beam velocity as embodied in certain forms of the invention.

In Fig. 1 a cathode ray tube I is provided, in known manner, with deflection systems 3 for the deflection of the cathode ray 2, and in this construction, the cathode ray tube I is closed at the front by a lens 4. As a deformable medium, a thin transparent skin or membrane 5 is stretched close behind the lens 4 and on the side facing the electron beam 2, the membrane 5, shown to a larger scale in Fig. 7, has small plates 6 which are separated from one another and are finely distributed, regularly or irregularly, over the entire surface, said small plates being constructed so that they are secondary-emitting on the side facing the cathode ray and light-reflecting on to the other side. An electrically-conducting gridlike electrode 8 connected with a control device. fo example, an amplifier valve I, is arranged on the membrane 5 on the side facing the lens 4. For clearness sake, the electrode 8 is shown coarse-meshed in Fig. 7 but comprises, in actual fact, a number of rods which is at least as large as the number of lines in the television picture. At a slight distance from the membrane 5, there is located the grid 9, which is also connected with the control device 1.

I0 is a light source, for example, an arc lamp. with an associated condenser H. Th objectiv l2 portrays the diaphragm l3 on a concave mirror II, in such a manner that the marginal rays l5 fall on the edges of'the mirror It, the latter portraying the objective l2 on the membrane 5 and the rays being limited by a diaphragm l6. Moreover. the lens 4, with the aid of the small plates 6 arranged on the membrane 5, portray the mirror I4 on itself when the membran 5 is not deformed. Finally, the membrane 5 is portrayed by the objective I! on the projection wall or screen [8.

W'I'he operation of the constructional example shown in Fig. 1 is as follows:

As already mentioned, when the membrane 5 is undeformed, the light projected from the light source through the mirror H on to the membrane 5 is thrown back again on to the mirror H and consequently no light reaches the projection screen l8. The cathode ray 2, however, now causes a deformation of the membrane 5 in the following manner.

For an explanation of the processes which now take place, it is necessary first to refer to Fig. 9.

In Fig. 9, the secondary emission factor a of the small plates 6 is represented as a function of the velocity of the electron beam as expressed in volts. By secondary emission factor a is to be understood the ratio of the number of secondarily emitted electrons to the number of impinging electrons.

The curve of a shows that with the potential U0, which amounts to a few thousand volts, equilibrium prevails between the impinging electrons and the secondary emitting electrons. This potential U will now adjust itself with the line-byline sweeping of the plates 6 by the cathode ray between the small plates 6 and the cathode. If the control device 1 should at any moment suppl the potential Us to the electrode 8, no deformation of the membrane will takeplace because there is no potential difference. If, however, a potential which differs from U0 is applied to the electrode 8 by the control device in consequence of the rapidly changing television signal, then all the small plates 6 receive the same potential in consequence of the capacitative effect. The electron beam will, however, immediatel change the small plates touched by it at this moment back to the potential U0. In this way, a potential difference arises between thes plates on the one hand and the electrode 8 on the other and thus provides an electrostatic force which deforms the membrane 5 at this place, by causing the grid-like electrode 8 to be drawn into the membrane and thereby divide the latter into elemental areas whose distortion converts them into lenses l9, as represented in Fig. 7. The difference in potential between the plates 6 and the electrode 8 will, however now be dependent upon the potential applied at the electrode 8. Thus,

' it can be attained that by means of the television signal applied to the electrode 8 in the form of a potential, lenses of greater or lesser curvature corresponding to the signal or the brightness values, respectively, are produced on the surface of the membrane 5.

For explaining the further processes, the path of the rays of a small lens 20 formed in the above-described manner is diagrammatically represented in Fig. 1.

As already described, when the membrane 5 is undeformed, the mirror It is portrayed on itself by the lens 4 with the aid of the reflecting plates 6. With the presence of the lens 20 formed .by the membrane '5, the image 21 of the mirror I4 is moved towards the lens 28 into the position indicated, for example by the double-headed arrow. The marginal rays 22 emanating from this image 2| now pass by the mirror ll, through the objective I] and on to the projection screen l8.

where there is formed a light spot 23 corresponding to the size of the lens 28. This spot is brighter, the more the lens is curved, because as the curvature of the lens 28 becomes greater, the image 2| moves still closer and consequently still greater marginal portions of the stream of light going out from the image 2| pass by the mirror M. The brightness distribution on the projection screen I8 corresponds to the deformation distribution of the membrane 5 and thus also to the brightness values of the television picture as given by the television signal. Finally, it may also be mentioned that an electrode must be provided for collecting the secondary electrons leaving the small plates 6, and in the example according to Fig. 1, this electrode is assumed to be the grid 9. It is obvious that any other deformable medium which is capable of being stretched out flat can be employed in place of the membrane 5, for example a crystal layer which is deformable by piezo-electric forces.

A further embodiment of the arrangement according to the invention is represented in Fig. 2, in which similar parts to those shown in Fig. 1 have the same reference numerals.

The example according to Fig. 2 corresponds essentially to that of Fig. 1, but differs from the latter by the small plates or lamellae 6 not being made light-reflecting, but instead are either translucent or have such large interstices that sufficient light can still pass through the membrane 5. In this way, the optical ray path is simplified by the objective 12 of Fig. 1 being omitted and the diaphragm i 3 being defined directly on the light collecting screen 24 by the lens 4, which is now arranged in front of the tube I. In other respects, the method of operation of this example corresponds exactly to that according to Fig. l.

The constructional example according to Fig. 3 differs from the example according to Fig. 1 in that two images are produced one after the other and side by side by the cathode ray 2, one of which is projected at the time whilst the other is recorded by the cathode ray. For this purpose, two ray paths are provided which correspond exactly to the example according to Fig. 1 and which are brought to coincidence on the projection screen.

What is new in this example is the rotating diaphragm 25, which covers that image which is in the course of being conceived or formed and allows the image which is ready for projection to pass through. It is obvious that even more than two ray paths with corresponding diaphragms could be provided,

The optical ray path of the example represented in Fig. 4 corresponds, in principle, to the example according to Fig. 2, apart from insignificant alterations. The diaphragm 13 in this construction is defined on the opening 21 in the mirror 28 by the lens 4 through the intermediary of the deflecting mirror 28, so that when the membrane 5 is undeformed, the total light passes through this opening 21 and the projection screen remains dark. The opening 2'! thus assumes the function of the concave mirror I4 in the example according to Fig. l and of the light collecting screen 24 in the example according to Fig. 2. Furthermore, the interceptor electrode 9 in this example is constructed as a cylinder.

An essential difference exists in the arrange- 7 ing the electron beam. The raster formation of the surface of the membrane is here produced by a carrier frequency intensity-modulation, to which reference has already been made. In this way, there occurs such a charge distribution on 4 the membrane 5 that a raster is formed which is disposed perpendicularly of the line direction. In addition to the intensity-modulation already mentioned for the formation of the raster, the velocity of the cathode ray is also controlled as in the example according to Fig. 1, for the purpose of producing the television picture or of changing the potential of the raster elements. This control is effected by the control device 1.

Finally, in the example according to Fig. 5, the optical ray path is selected to be exactl the same as in the example according to Fig, 4. Once again, however, the type of the deformation or of the production of lenses is diiferent from the previous examples. The raster formation on the membrane 5 is again produced by carrier-frequenc intensity-modulation, as in the example according to Fig. 4, but the change of potential of the raster elements is no longer caused by secondar emission, but by discharging the charges through the membrane 5 to the electrode 25, this being attained by imparting Due to the leaking off or discharge of the charges, the rastering of the membrane disappears after a definite time determined by the conductivity of the medium, so that the electron beam has the opportunity during the subsequent sweeping of the membrane, to set up or apply the new charge distribution in accordance with a new television picture. In this example, the membrane 5 is not specially prepared for secondary emission. However, since it is physically impossible to find suitable materials without any secondary emission, the occurrence of "stray" electrons caused by secondary emission is prevented in the example by a negatively charged screen 30 opposite the membrane 5. This screen could most easily consist of a stationary sieve, but it would then also be portrayed on the projection screen I8 by the objective I]. Consequently, in the present example, the screen is constructed as a rotating disc, which is illustrated in Fig. 6. This disc shows alternatively, for example, extremely thin metal foils 3| and grids 32, and rotates in synchronism with the movement of the electron beam 2 in such a manner that the electron beam, during the production of the raster, always reaches the membrane 5 only through one of the thin foils 3|. As is known, an electron beam is weakened only to an immaterial extent by the passage through thin metal foils, more particularly aluminum foils.

Finally, in Fig. 5, there is provided a special electron source 33 which throws a uniformlydistributed electron beam 34 that is, a nonfocused beam on to the membrane 5, and thereby produces a constant surface charge thereon. This surface charge serves to keep the membrane 5 under a constant mechanical bias and thus to strengthen the action of the rastered charge distribution applied by the cathode ray.

In the foregoing remarks, the formation of cylinder-shaped lenses or mirrors has always been discussed, because this form has proved to be most favourable for the practial construction. It is however, to be mentioned that the raster forming electrode 8 in Fig. 7, could, for example, also be so constructed that round, elliptical or polygonal lenses are formed.

In the examples according to Figs. 4 and 5, it would also be possible to effect the rastering by simple splitting up of the cathode ray into a plurality of recording part-rays distributed sideby-side over the height of the line, instead of by carrier-frequency modulation of the cathode ray. Furthermore, in the examples according to Figs. 4 and 5, it would also be possible to use, instead of a deformable membrane 5, a liquid layer whose surface is deformed. It is also obvious that media having different layers, for example, membrane and liquid, are also capable of being utilised.

Finally, in Fig. 8, a further .possible construction of the membrane is shown which can be used with particular advantage in the examples according to Figs. 4 and 5. On the side away from the cathode ray, the membrane 5 shows a gridlike electrode 35, whereas on the other side, the pressure-producing charges are set up by the electron beam. Since here the rastering of the medium is again undertaken by the electrode, it is no longer necessary in this case to apply the charges themselves in rastered formation.

The possibilities of the invention are not exhausted by the constructional examples illustrated. Further combinations, particularly of c A1 I "n. A A a "la"- the constructional examples with one anut c1 can also be devised without departing from the scope of the invention. a

1 claim:

1. Apparatus for the reproduction of a television picture, characterised by a cathode ray tube with at least two ray-deflecting systems and at least one control device for the cathode ray. and containing a medium which is stretched out flat in the form of a screen and which is deformable by static electric forces within successive elemental areas to provide numerous lens surfaces. said medium being provided with at least one electrically conducting electrode, and a separate light source from which the light is projected. by lens and mirror systems, to the medium of the cathode ray tube and thence on to the projection screen by way of at least one objective, the arrangement being so contrived that no light from the separate light source reaches the projection screen from raster elements, the deformation of which corresponds to the brightness 0.

2. Apparatus as claimed in claim 1, wherein an auxiliary electrode is disposed in the immediate vicinity of the medium which is stretched out flat.

3. Apparatus as claimed in claim 1. wherein an auxiliary electrode which is at least in part a grid is disposed in the immediate vicinity of the medium which is stretched out fiat.

4. Apparatus as claimed in claim 1, wherein an auxiliary electrode which is at least in part a metal foil is disposed in the immediate vicinity of the medium which is stretched out flat.

5. Apparatus as claimed in claim 1, wherein a movable auxiliary electrode is disposed in the immediate vicinity of the medium which is stretched out fiat.

6. Apparatus as claimed in claim 1, wherein an auxiliary electrode movable in synchronism with the image-deflection of the cathode ray is disposed in the immediate vicinity of the medium which is stretched out flat.

7. Apparatus as claimed in claim 1, wherein the medium is elastically deformable.

8. Apparatus as claimed in claim 1, wherein the medium consists of a highly polymeric substance with low elasticity modulus.

9. Apparatus as claimed in claim 1, including a, se arate electron source which, for the purpose of producing suitably directed electrical surface forces in the medium provides an electric current which is uniform as regards time and place.

FRIEDRICH ERNST FISCHER. 

